1. Field
Apparatuses consistent with exemplary embodiments relate to a part holding head assembly for a chip mounting device, and more particularly, to a part holding head assembly of a part mounting device mounting an electronic part, the part holding head assembly including a nozzle configured to hold the electronic part such as an integrated circuit (IC) chip or the like, on a substrate.
2. Description of the Related Art
In the related art, a part mounting device moves a part holding head assembly above a part supply unit and enables a nozzle of the part holding head assembly to perform descending and ascending operations at that location. Thereafter, the part mounting device adsorbs a part at a lower end of the nozzle in a vacuum to pick up the part, moves the part holding head assembly above a substrate, and enables the nozzle to re-perform the descent or ascent operation so as to mount the part in a preset coordinate position of the substrate.
During the operation described above, if the descending and ascending operations of the nozzle are performed to pick up the part into the nozzle, and an ascent stroke of the nozzle is too strong, the lower end of the nozzle may press on an upper surface of the part with an extensive force and thus may break the part. If the descent stroke is too weak, the nozzle may fail to contact the upper surface of the part and thus may fail to pick up the part. Further, if the descent stroke of the nozzle is too strong, the part adsorbed at the lower end of the nozzle may be pressed with an extensive force and may be broken on the substrate. Meanwhile, if the descent stroke is too weak, the part held in the nozzle fails to contact the upper surface of the substrate and thus fails to mount the part. Therefore, the descent stroke of the nozzle should be accurately controlled.
As a method of accurately controlling an ascent/descent stroke of a nozzle, Japanese Patent No. 3543044 discloses a method of using a sensing unit (a contact detecting sensor) for sensing a contact of a nozzle.
As another method of accurately controlling a descent stroke of a nozzle, Japanese Patent Application No. 2013-212220 discloses a method of using a reflective light sensor (an optical fiber sensor) as a contact detecting sensor. The optical fiber sensor includes a light-emitting unit which emits light toward an outside reflective surface of the nozzle, a light-receiving unit that receives reflected light reflected from the outer reflective surface, and a sensor unit that continuously measures a received amount of reflected light. When the received amount decreases to be lower than or equal to a threshold value, the optical fiber sensor determines that the nozzle contacts a part to generate a contact sensing signal.
In other words, light emitted from the light-emitting unit of the optical fiber sensor is focused on the reflective surface before the nozzle contacts the part. Therefore, if upper and lower positions of the nozzle are changed due to a contact of the nozzle with the part, an amount of reflected light reflected from the reflective surface decreases, and an amount of light received by the light-receiving unit of the optical fiber sensor decreases. In the related art, an amount of received light by the light receiving unit is compared with a predetermined threshold value, and when the amount of received light by the light receiving unit decreases to be lower than or equal to the threshold value, the optical fiber sensor determines that the nozzle contacts the part and thus stops descending of the nozzle based on the determination.
In the related art, the threshold value is set to a fixed value based on a pre-experimental result using an optical fiber sensor. Therefore, each type of different nozzles requires the pre-experimental results on the threshold value A. Also, as a nozzle is used, foreign material may become stuck onto a reflective surface of the nozzle. Therefore, before the same nozzle contacts a part, an amount of received light may be changed as time elapses. If an amount of received light is changed according to a nozzle or a time elapse before a nozzle contacts a part as described above, and the threshold value A is set to a fixed value, the following problems occur.
If, for example, an amount of received light, which is measured before a nozzle contacts a part, is lower than the threshold value A, an optical fiber sensor erroneously determines that the nozzle contacts the part when the nozzle actually does not contact the part. In this case, before the nozzle actually contacts the part, a picking-up (adsorbing) operation or a mounting operation of the part starts, and thus a picking-up error or a mounting error occurs. Also, the nozzle may be in a state where a contact of the nozzle may not be sensed.
If, for example, an amount of received light is significantly higher than the threshold value before a nozzle contacts a part, the amount of received light does not each a value lower than or equal to the threshold value even after the nozzle contacts the part. Therefore, although the amount of received light decreases, the amount of received light takes a long time to reach the threshold value A. As a result, a long time is taken from when the nozzle contacts the part to when the nozzle stops, and thus the nozzle excessively presses on the part, and the part may be damaged. In other words, the pressing of the nozzle onto the part may not be accurately controlled.
A contact sensing function performed by an existing contact detecting sensor (or an optical fiber sensor) is not sufficient for an adaptability to a change in an amount of received light before the nozzle contacts the part due to a difference in a shapes or status of the nozzle or the like. In other words, a robust performance of contact sensing function is still desired.
Also, in the related art, an outside reflective surface of a nozzle may become dirty or a reflective plate may be installed to form a reflective surface in the nozzle. In this case, a sufficient amount of received light may not be acquired from before the nozzle contacts the part. Therefore, a contact of the nozzle may not be sensed or although the contact of the nozzle is sensed, an accuracy of the contact of the nozzle is lowered.
Therefore, an optical abnormality of a nozzle, cleanness of a reflective surface, uninstalling of the reflective surface, or the like, needs to be accurately sensed in real time to accurately sense a contact of the nozzle through a contact detecting sensor, such as an optical fiber sensor that is a reflective optical fiber sensor, or the like.